Ion implanters are commonly used in the production of semiconductor wafers. An ion source is used to create an ion beam, which is then directed toward the wafer. As the ions strike the wafer, they dope a particular region of the wafer. The configuration of doped regions defines their functionality, and through the use of conductive interconnects, these wafers can be transformed into complex circuits.
A block diagram of a representative ion implanter 100 is shown in FIG. 1. An ion source 110 generates ions of a desired species. In some embodiments, these species are atomic ions, which may be best suited for high implant energies. In other embodiments, these species are molecular ions, which may be better suited for low implant energies. These ions are formed into a beam, which then passes through a source filter 120. The source filter is preferably located near the ion source. The ions within the beam are accelerated/decelerated in column 130 to the desired energy level. A mass analyzer magnet 140, having an aperture 145, is used to remove unwanted components from the ion beam, resulting in an ion beam 150 having the desired energy and mass characteristics passing through resolving aperture 145.
In certain embodiments, the ion beam 150 is a spot beam. In this scenario, the ion beam passes through a scanner 160, which can be either an electrostatic or magnetic scanner, which deflects the ion beam 150 to produce a scanned beam 155-157. In certain embodiments, the scanner 160 comprises separated scan plates in communication with a scan generator. The scan generator creates a scan voltage waveform, such as a sine, sawtooth or triangle waveform having amplitude and frequency components, which is applied to the scan plates. In a preferred embodiment, the scanning waveform is typically very close to being a triangle wave (constant slope), so as to leave the scanned beam at every position for nearly the same amount of time. Deviations from the triangle are used to make the beam uniform. The resultant electric field causes the ion beam to diverge as shown in FIG. 1.
In an alternate embodiment, the ion beam 150 is a ribbon beam. In such an embodiment, there is no need for a scanner, so the ribbon beam is already properly shaped.
An angle corrector 170 is adapted to deflect the divergent ion beamlets 155-157 into a set of beamlets having substantially parallel trajectories. Preferably, the angle corrector 170 comprises a magnet coil and magnetic pole pieces that are spaced apart to form a gap, through which the ion beamlets pass. The coil is energized so as to create a magnetic field within the gap, which deflects the ion beamlets in accordance with the strength and direction of the applied magnetic field. The magnetic field is adjusted by varying the current through the magnet coil. Alternatively, other structures, such as parallelizing lenses, can also be utilized to perform this function.
Following the angle corrector 170, the scanned beam is targeted toward the workpiece 175. The workpiece is attached to a workpiece support. The workpiece support provides a variety of degrees of movement.
The workpiece support is used to both hold the wafer in position, and to orient the wafer so as to be properly implanted by the ion beam. To effectively hold the wafer in place, most workpiece supports typically use a circular surface on which the workpiece rests, known as a platen. Often, the platen uses electrostatic force to hold the workpiece in position. By creating a strong electrostatic force on the platen, also known as the electrostatic chuck, the workpiece or wafer can be held in place without any mechanical fastening devices. This minimizes contamination and also improves cycle time, since the wafer does not need to be unfastened after it has been implanted. These chucks typically use one of two types of force to hold the wafer in place: coulombic or Johnson-Rahbeck force.
The workpiece support typically is capable of moving the workpiece in one or more directions. For example, in ion implantation, the ion beam is typically a scanned or ribbon beam, having a width much greater than its height. Assume that the width of the beam is defined as the x axis, the height of the beam is defined as the y axis, and the path of travel of the beam is defined as the z axis. The width of the beam is typically wider than the workpiece, such that the workpiece does not have to be moved in the x direction. However, it is common to move the workpiece along the y axis to expose the entire workpiece to the beam.
In some applications, it is necessary to pass fluids, in the form of gas and/or liquid into the vacuum environment. For example, in some embodiments, the platen is maintained at a constant, or nearly constant temperature, by running fluid through conduits located within the platen. Depending on the type of ion implantation being performed, this fluid may be for the purpose of heating the workpiece or cooling the workpiece.
This entire system is typically maintained at very low pressure, such as less than 100 mTorr. Although the pressure is greater than 0, this environment is commonly referred to as a vacuum. The task to delivering fluids to a vacuum environment is further complicated by several factors. First, in many instances, the fluid must be delivered to a terminus or endpoint that is not stationary. As described above, it is typical for the workpiece support to move along the y axis to irradiate the entire surface of the workpiece. The movement of the terminus typically necessitates the use of flexible tubing or some other moveable conduit. Making this endeavor even more difficult, at times the fluids that are being delivered are at very low temperatures, such as cryogenic temperatures. In extremely low temperatures, the flexible tubing is susceptible to fatigue due to the bending stresses from the cyclic movement, and therefore cannot be used. Alternative coupling mechanisms, such as rotary or linear sliding seals, are difficult to produce without leakage. They are also typically physically quite large and hence difficult to package near the moving workpiece.
As an example, for cryogenic ion implantation, it is necessary to maintain the temperature of wafer at very low temperatures, despite the fact that constant ion bombardment tends to increase its temperature. One method of achieving this is to pass low temperature fluids through conduits in the platen. By keeping the platen extremely cold, the wafer, by virtue of its contact with the platen, preserves its low operating temperature. However, as explained above, the wafer (and therefore the platen) is typically moved axially through the ion beam so as to insure that the entire wafer is exposed to the ion beam. Reliably delivering cryogenic fluid to a moving platen in a vacuum environment is extremely difficult.
These constraints make it very different to provide a fluid delivery system to a workpiece support, such as a platen, in a vacuum wafer processing system. Therefore, a system that allows the delivery of fluid, such as extremely cold fluid, into a vacuum environment would be extremely beneficial, especially if delivered to a non-stationary terminus.